diff --git a/src-tauri/src/proxy/providers/claude.rs b/src-tauri/src/proxy/providers/claude.rs
index 6443f70a0..c8db6b919 100644
--- a/src-tauri/src/proxy/providers/claude.rs
+++ b/src-tauri/src/proxy/providers/claude.rs
@@ -225,78 +225,12 @@ pub fn normalize_anthropic_messages_for_provider(
         return false;
     }
 
-    let mut changed = normalize_anthropic_system_role_messages(body);
-    changed |= normalize_anthropic_tool_thinking_history_for_provider(body, provider, api_format);
+    let mut changed =
+        normalize_anthropic_tool_thinking_history_for_provider(body, provider, api_format);
     changed |= normalize_deepseek_thinking_disabled_strip_effort(body, provider);
     changed
 }
 
-fn normalize_anthropic_system_role_messages(body: &mut Value) -> bool {
-    let mut system_parts = Vec::new();
-    let changed = {
-        let Some(messages) = body.get_mut("messages").and_then(Value::as_array_mut) else {
-            return false;
-        };
-
-        let original_len = messages.len();
-        let mut kept_messages = Vec::with_capacity(messages.len());
-        for message in std::mem::take(messages) {
-            if message.get("role").and_then(Value::as_str) == Some("system") {
-                if let Some(content) = message.get("content") {
-                    append_anthropic_system_parts(content, &mut system_parts);
-                }
-            } else {
-                kept_messages.push(message);
-            }
-        }
-
-        let changed = kept_messages.len() != original_len;
-        *messages = kept_messages;
-        changed
-    };
-
-    if !changed || system_parts.is_empty() {
-        return changed;
-    }
-
-    let mut merged_parts = Vec::new();
-    if let Some(existing) = body.get("system") {
-        append_anthropic_system_parts(existing, &mut merged_parts);
-    }
-    merged_parts.extend(system_parts);
-
-    if !merged_parts.is_empty() {
-        body["system"] = Value::Array(merged_parts);
-    }
-
-    true
-}
-
-fn append_anthropic_system_parts(content: &Value, parts: &mut Vec<Value>) {
-    match content {
-        Value::String(text) if !text.trim().is_empty() => {
-            parts.push(json!({
-                "type": "text",
-                "text": text
-            }));
-        }
-        Value::Array(items) => {
-            for item in items {
-                append_anthropic_system_parts(item, parts);
-            }
-        }
-        Value::Object(obj)
-            if obj
-                .get("text")
-                .and_then(Value::as_str)
-                .is_some_and(|text| !text.trim().is_empty()) =>
-        {
-            parts.push(Value::Object(obj.clone()));
-        }
-        _ => {}
-    }
-}
-
 fn normalize_anthropic_tool_thinking_history(body: &mut Value) -> bool {
     let Some(messages) = body.get_mut("messages").and_then(Value::as_array_mut) else {
         return false;
@@ -2189,7 +2123,10 @@ mod tests {
     }
 
     #[test]
-    fn test_anthropic_system_role_messages_move_to_top_level_system() {
+    fn test_anthropic_messages_no_longer_hoists_system_role_messages() {
+        // After reverting #3775, role=system messages are left in `messages[]`
+        // (DeepSeek's endpoint accepts them natively) and the top-level `system`
+        // field is untouched, preserving the request prefix.
         let provider = create_provider(json!({
             "env": {
                 "ANTHROPIC_BASE_URL": "https://api.deepseek.com/anthropic",
@@ -2211,15 +2148,13 @@ mod tests {
 
         let changed = normalize_anthropic_messages_for_provider(&mut body, &provider, "anthropic");
 
-        assert!(changed);
+        assert!(!changed);
         let messages = body["messages"].as_array().unwrap();
-        assert_eq!(messages.len(), 1);
-        assert_eq!(messages[0]["role"], "user");
-
-        let system = body["system"].as_array().unwrap();
-        assert_eq!(system[0]["text"], "Existing top-level system.");
-        assert_eq!(system[1]["text"], "Message system one.");
-        assert_eq!(system[2]["text"], "Message system two.");
+        assert_eq!(messages.len(), 3);
+        assert_eq!(messages[0]["role"], "system");
+        assert_eq!(messages[1]["role"], "user");
+        assert_eq!(messages[2]["role"], "system");
+        assert_eq!(body["system"], "Existing top-level system.");
     }
 
     #[test]